Temperature Fluctuations And Reloading Brass-Part 2

If you haven’t read part one of this article, it is
suggested you go ahead and do so now.

With frozen-ammo velocities in the bag, I then shot the ammo
still cooking on the dashboard of my pickup. The cartridges were hot to the
point of being uncomfortable to hold.

The result? The answer to the first of our threefold
question is yes: Temperature extremes do affect velocity. Both propellant types
shot significantly higher velocities with the hot ammunition.

The answer to the second question is also yes: The disparity
was much less with one propellant brand/type than with the other. Specifically,
H-1000 had 44 fps disparity between temperature extremes; RL-22 had 130 fps
disparity. The difference between propellant types — 86 fps — was significant.

As an aside, an effect I didn’t foresee was that hot
ammunition — at least in this case — is more consistent than cold ammo. Take
note of the far tighter extreme spreads and standard deviations.

To answer the last of our threefold question (is
temperature-induced variation enough to cause a miss at hunting ranges) we need
to run some ballistic calculations. Keeping things very simple, I used the
calculator on Hornady’s website and plugged in the appropriate
numbers. Here’s what I found:

With RL-22 powder and a 200-yard zero, the 160-grain Nosler
AccuBond (B.C. .531) will drop 18.8 inches at 400 yards with the frozen ammo
and 17.1 inches with the hot ammo. The difference is less than two inches. With
H-1000 the difference is less than one inch. So the answer is no: When using a
temperature-sensitive propellant, even extreme swings in temperature won’t
cause enough disparity in point of impact to make us miss a game animal.

How about for long-range shooters that really stretch the
distance? Let’s double the distance and run the numbers:

Again with RL-22, the projectile drops 144.5 inches with the
frozen ammo and 131.2 inches with the hot ammo. The difference is 13.3 inches,
which is certainly enough to cause a complete miss on a deer-size animal, and a
miss — or worse, a wound — on an elk-size animal. Clearly, as distances
stretch, temperature sensitivity becomes far more critical.

Let’s look at H-1000: At 800 yards, the bullet drops 153.8
inches with the frozen ammo and 148.6 inches with the hot ammo. The difference
is much less, only 5.2 inches. Depending on the size of the game, that’s still
enough to potentially cause a miss, but the disparity is more acceptable.

We don’t have space to address it here, but another element
that exerts additional drag and drop on cold ammunition is the density of
colder air. Lower temperatures result in more drag on your bullet, which will
open up the disparities shown above even more.

The multifaceted nature of this “fact or fiction” topic bars
a simple yes or no answer, but we can come away with this:

Yes, temperature does affect velocity, and it affects
some propellants more than others.

However, within common hunting distances out to 400
yards or so, the disparities are little enough that we don’t need to worry
about them.

If you shoot long range, though, you’d better be familiar
with your velocities and the trajectory of your bullet in the conditions in
which you’ll likely shoot. If you hunt in very cold weather, get out and
practice in very cold weather. Leave your rifle and ammunition out to freeze
overnight, and chronograph your ammunition. Then plug those numbers into your
ballistic app.